This invention relates generally to apparatus, methods and systems for monitoring fluid in containers. The present invention relates more particularly, but not by way of limitation, to a radio-linked fluid monitoring system incorporating apparatus and method that use a single pressure sensor in a respective container to determine fluid level from which fluid volume can be automatically determined for different shapes of container.
To maintain an adequate fluid supply for a process which draws fluid held in a storage container, the amount of fluid in the container typically must be monitored. In the oil and gas industry, for example, a well sometimes needs to be fractured to enhance its productivity. Fracturing fluid to accomplish this is typically stored in one or more storage containers at the well site. The fluid is pumped out of the containers and into the well as needed. The operator in charge of the pumping needs to be aware of the various conditions of the pumping and fracturing process, one of which conditions is the amount of fluid remaining in the one or more containers.
One way to remain apprised of the amount of fluid is for the operator to visually or otherwise locally inspect each fluid container. This is not a desirable technique because of the potential safety hazard of being on or around the containers to inspect them and because of the time it would take to inspect the containers.
To alleviate the foregoing shortcoming, there are automated devices for measuring fluid levels in containers. These can use various techniques, but the one relevant to our invention described below uses fluid pressure for determining the amount of fluid in the container. The pressure responsive techniques we are aware of use two pressure sensors to determine fluid level. One type uses one differential pressure transducer to determine density and one gauge pressure transducer to sense pressure at the bottom of the body of fluid. Another type uses two gauge pressure transducers; outputs from the two pressure transducers spaced a known distance apart are used to compute density, and the output from one of the pressure transducers provides the total fluid pressure which is divided by the determined density to give a quotient specifying the level of the fluid in the container. The transducers of these systems we are aware of are fixed to the containers (e.g., attached to the side wall of the container below the surface of the contained fluid) so that they cannot be readily moved (e.g., container must be drained before transducers can be detached). Such systems can provide for remote communications of data via wire or radio frequency transmission.
Although the foregoing automated devices and systems can provide advantages over types requiring local inspections by an operator, there is still the need for an improved automated apparatus. There is the need for a fluid monitoring apparatus which uses only a single pressure sensor, thereby obviating the cost of the second sensor used in the aforementioned devices. There is the need for a fluid monitoring apparatus which is easy to use with different types of containers. For example, the apparatus preferably should be portable and adaptable for use with different shapes of containers. That is, the apparatus should be able not only to calculate the height of the fluid in a container, but also to convert that height into the correct volume, which can be different from one shape of container to another for the same calculated height. There is also the need for a fluid monitoring method and system which meet these same needs and which permit remote communication and control.